Secondary battery and method of manufacturing the same

ABSTRACT

A secondary battery according to an embodiment includes a container having a pouring hole through which an electrolyte is poured, and housing the electrolyte, poured through the pouring hole, together with an electrode body; and a sealing lid fixed to the container and closing the pouring hole. The container has a plurality of grooves extending in parallel along the outer edge of the pouring hole, in a predetermined region that surrounds the periphery of the pouring hole, and the sealing lid is provided on the plurality of grooves in such a manner as to close the pouring hole and is fixed to the container.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 13/356,357filed on Jan. 23, 2012, which is based on and claims the benefit ofpriority from Japanese Patent Applications No. 2011-12675, filed on Jan.25, 2011 and No. 2011-245192, filed on Nov. 9, 2011; the entire contentsof which are incorporated herein by reference.

FIELD

Embodiments herein relate to a secondary battery and a method ofmanufacturing a secondary battery.

BACKGROUND

In recent years, secondary batteries represented by a lithium ionbattery have increasingly wide range of applications, mainly forin-vehicle use, and the production volume is constantly increasing. Inthe process of manufacturing a secondary battery, a method is oftenemployed, in which the components of the battery are sealed in a metalcase. In addition, in order to improve the space efficiency of thesecondary battery, a rectangular cell case is often employed rather thana conventional circular case. In both cases where the circular cell caseis employed and where the rectangular cell case is employed, laserwelding, by which a structural body can be manufactured efficiently, ismore often used for manufacturing lithium ion batteries.

In the manufacturing process of a lithium ion battery, laser welding isoften used in the following three processes:

1. Cap seam welding for bonding an aluminum can body and a cap member.

2. Seal welding for closing a pouring hole for pouring an electrolyte.

3. Component welding for electrically connecting a plurality of cells inparallel or in series.

However, the seal welding of the second process among theabove-mentioned processes is known to be technically difficult becausethe surroundings of the pouring hole, which tend to be easilycontaminated with an electrolyte, need to be welded by a laser. When ametal lid for sealing is placed and welded on the pouring hole with someadhering electrolyte thereon, a weld defect occurs due to the influencean electrolyte or a solvent contained in the electrolyte. Even whenwelding is performed after removing the adhering electrolyte by suctionor wiping, a bonding defect possibly due to the electrolyte will occurat a certain rate.

FIG. 1 is an external perspective view showing a schematic configurationof a secondary battery according to an embodiment.

FIG. 2 is an enlarged plan view showing a periphery of a sealing lid ofa container included in the secondary battery shown in FIG. 1.

FIG. 3 is a cross-sectional view taken along a line A1-A1 in FIG. 2.

FIG. 4 is an explanatory view for explaining a starting end and aterminal end of a groove shown in FIGS. 2 and 3.

FIG. 5 is a flowchart showing the flow of a manufacturing process formanufacturing the secondary battery shown in FIG. 1.

FIG. 6 is an explanatory view for explaining laser irradiation in themanufacturing process shown in FIG. 5.

FIG. 7 is a plan view depicting a welding mark on the sealing lid shownin FIG. 2.

FIG. 8 is an explanatory view for explaining a welding mark formed by CWlaser beam irradiation, and a welding mark formed by pulse laser beamirradiation.

DETAILED DESCRIPTION

A secondary battery according to an embodiment includes a containerhaving a pouring hole through which an electrolyte is poured, andhousing the electrolyte, poured through the pouring hole, together withan electrode body; and a sealing lid fixed to the container and closingthe pouring hole. The container has a plurality of grooves extending inparallel along the outer edge of the pouring hole, in a predeterminedregion that surrounds the periphery of the pouring hole, and the sealinglid is provided on the plurality of grooves in such a manner as to closethe pouring hole while being fixed to the container.

According to another embodiment, a method of manufacturing a secondarybattery includes: forming a plurality of grooves by laser irradiation ina predetermined region surrounding a periphery of a pouring hole of acontainer in which an electrolyte has been poured, the plurality ofgrooves extending in parallel along the outer edge of the pouring hole;placing a sealing lid on the formed plurality of grooves in such amanner as to close the pouring hole; and fixing the placed sealing lidto the container by laser welding.

Various Embodiments will be described hereinafter with reference to theaccompanying drawings.

An embodiment is described with reference to the drawings.

As shown in FIG. 1, a secondary battery 1 according to the presentembodiment includes an electrode body 2, a container 3 housing theelectrode body 2 together with an electrolyte, and a pair of a positiveelectrode terminal 4 and a negative electrode terminal 5. The secondarybattery 1 is, for example, a non-aqueous electrolyte secondary batterysuch as a lithium ion battery.

The electrode body 2 is formed by winding positive and negativeelectrode sheets as power generation elements in a spiral shape with aseparator being interposed between the electrode sheets. The electrodebody 2 is housed in the container 3 together with the electrolyte.

The container 3 is an outer container in a flat rectangularparallelepiped shape, and is formed of, for example, a metal such asaluminum or an aluminum alloy. The container 3 has a one-end-opencontainer body 3 a having an opening at the upper end (in FIG. 1), and alid body 3 b having a rectangular plate shape for closing the opening ofthe container body 3 a, and is liquid-tightly formed with the lid body 3b being welded to the container body 3 a.

The positive electrode terminal 4 is provided at one end of the lid body3 b in the longitudinal direction, and the negative electrode terminal 5is provided at the other end. The positive electrode terminal 4 and thenegative electrode terminal 5 are respectively connected to the positiveelectrode and the negative electrode of the electrode body 2, andproject from the upper surface of the lid body 3 b. In addition, eitherone of the terminals, for example, the positive electrode terminal 4 iselectrically connected to the lid body 3 b to have the same potential asthat of the container 3. The negative electrode terminal 5 extendsthrough the lid body 3 b, and a seal member made of an insulatingmaterial such as a synthetic resin or glass, for example, a gasket (notshown) is provided between the negative electrode terminal 5 and the lidbody 3 b. The seal member hermetically seals between the negativeelectrode terminal 5 and the container 3, while electrically insulatingthe negative electrode terminal 5 from the container 3.

A safety valve 6 having, for example, a rectangular shape is provided inthe center portion of the lid body 3 b. The safety valve 6 is formed bythinning a portion of the lid body 3 b to approximately half thethickness of the other portion of the lid body 3 b, and a stamp isformed in the middle of the upper. surface of the thinned portion. Inthe case where the internal pressure of the container 3 exceeds apredetermined value because of generation of gas inside the container 3due to a failure or the like of the secondary battery 1, the safetyvalve 6 is opened to release the gas inside the container 3 and to thusreduce the internal pressure of the container 3, thereby preventing afailure such as an explosion of the secondary battery 1.

Furthermore, a pouring bole 7 through which the electrolyte is pouredinto the container 3 is formed in the lid body 3 b. The pouring hole 7is a through-hole, and is formed in, for example, a circular shape. Theelectrolyte is poured into the container 3 through the pouring hole 7.

As shown in FIGS. 2 and 3, a plurality of grooves 8 that extend inparallel along the outer edge of the pouring hole 7 are formed in thelid body 3 b. The grooves 8 are formed in a predetermined regionincluding the pouring hole 7 on the surface of the lid body 3 b, i.e., apredetermined region R1 which surrounds the periphery of the pouringhole 7. The predetermined region R1 is, for example, a circular regionconcentric to the pouring hole 7, with a radius of several mm which isgreater than that of a sealing lid 9. The grooves 8 are arranged in thedirection of the normal to the outer edge of pouring hole 7, i.e., inthe direction of the radius, between the outer edge of the pouring hole7 and the outer edge of the predetermined region R1, and thus form agroove region. The grooves 8 are formed by a single groove existing in aspiral shape (helical shape}, however, the formation of the grooves 8 islimited to this manner, and the grooves 8 may be formed by, for example,a plurality of grooves.

Here, the grooves 8 are termed by irradiating the predetermined regionR1 on the lid body 3 b surrounding the periphery of the pouring hole 7with a laser beam in a spiral pattern, and thus are formed of a singlegroove in a spiral shape. In this step, a laser beam having a sufficientoutput to melt the metal is irradiated. As shown in FIG. 4, a startingpoint P1 of the laser irradiation is located adjacent to the outer edgeof the pouring hole 7, and the laser beam irradiation is performed fromthe inside to the outside in a spiral pattern, and thus a terminal pointP2 of the laser irradiation is located on the outer edge of thepredetermined region R1. At first, the starting end of the groove 8corresponding to the starting point P1 of the laser irradiation has asemicircular arc shape. However, when another groove a which is adjacentto the starting point P1 is formed, the other groove 8 overlaps with thestarting point P1, and thus the original semicircular arc shape isdeformed to be an arc shape which is shorter than the semicircular arc.On the other hand, the terminal end of the grooves 8 corresponding tothe terminal point P2 of the laser irradiation is located on theoutermost circumference, and thus has a semicircular arc shape unlikethe starting end.

The sealing lid 9 that closes the pouring hole 7 is fixed to the lidbody 3 b by laser welding. The sealing lid which is formed of, forexample, a metal such as aluminum or an aluminum alloy is provided onthe relevant grooves 8 in such a manner as to close the pouring hole 7,and is fixed to the lid body 3 b. The sealing lid 9 is formed, forexample, in a circular shape with its radius being greater than theradius of the pouring hole 7 and being less than the radius of thepredetermined region R1.

Next, a manufacturing process (manufacturing method) for theabove-mentioned secondary battery 1 is described.

As shown in FIG. 5, at first, an electrolyte is poured through thepouring hole 7 into the container 3 using an electrolyte pouring device(Step S1). Subsequently, the container 3 in which the electrolyte hasbeen poured is provided to a laser irradiation device (Step S2).

Next, the ambient atmosphere of the container 3 in which the electrolytehas been poured is put in a reduced pressure state (Step S3). Note that,the entire container 3 or only the upper portion thereof where thesealing lid 9 is located is enclosed in an enclosed space, i.e., isenclosed in a chamber of the laser irradiation device. The atmosphere ofthe enclosed space within the chamber is reduced in pressure to, forexample, 20 kPa in N₂ atmosphere.

After the pressure reduction in Step S3, the surrounding periphery (theabove-described predetermined region R1) of the pouring hole 7 on thecontainer 3 is irradiated with a laser beam using the laser irradiationdevice, so that each groove 8 is formed in the predetermined region R1on the lid body 3 b of the container 3 (Step S4).

In this step, as shown in FIG. 6, the predetermined region R1 on the lidbody 3 b is irradiated from the inside to the outside in a spiralpattern with a laser beam having a sufficient output to melt the metalusing a laser irradiation unit 11 of the laser irradiation device. Thus,a single groove in a spiral shape is formed, and consequently, theplurality of grooves 8 that extend in parallel along the outer edge ofthe pouring hole 7 are formed. At the same time, because of the heatgenerated as the metal is melted by a laser beam, the electrolyteadhering to the periphery of the pouring hole 7 is vaporized andremoved. In the case where the adhering electrolyte is not removed andthe sealing lid 9 is welded to the lid body 3 b using a laser in asubsequent process, a weld defect such as a defective hole frequentlyoccurs.

Note that the laser irradiation device extracts an image of the pouringhole 7 from data of a captured image of a periphery (a region includingthe predetermined region R1) of the pouring hole 7, in advance, andperforms image processing on the extracted image of the pouring hole 7to identify the coordinates of the pouring hole 7. Then, the laserirradiation device focuses a laser beam having a sufficient output tomelt the metal, and then scans and irradiates the periphery of thepouring hole 7 in a spiral pattern with the laser beam, while correctingthe laser irradiation position based on the identified coordinates.

As the laser beam scanning method, a scanning method using a scannersuch as a galvano scanner is preferable because high-speed laser beamscanning is possible with the method. However, a method of rotating thework body of the container 3, or a method of moving an optical systemusing a moving mechanism such as a robot may be used.

Note that overflowed electrolyte in the periphery of the pouring hole 7of the container 3 may be absorbed by an absorber before the grooves 8are formed. In this case, the electrolyte adhering to the periphery ofthe pouring hole 7 can be securely removed. In the case where the upperend of the through pouring hole 7 is formed in a tapered shape, thegrooves a may be formed starting from the tapered upper end.

Next, after the formation of the grooves 8 in Step S4, the sealing lid 9is placed on the relevant grooves 8 of the lid body 3 b of the container3 in such a manner as to close the pouring hole 7 by a mounting devicesuch as a robot (Step S6). In the above-mentioned reduced pressurestate, the sealing lid 9 is fixed to the lid body 3 b of the container 3by laser welding (Step S6). Finally, a predetermined inspection such asa shipment test is performed (Step S7).

In the laser welding, the laser irradiation device uses the laserirradiation unit 11 to irradiate the surface area of the sealing lid 9above the lid body 3 b in a ring pattern with a laser beam having asufficient output to melt the metal, higher than the laser output usedfor the above-described formation of the grooves 8 (for example, abouttwice as much as the laser output used for the formation of the grooves8). Consequently, the outer edge of the pouring hole 7 is irradiatedwith a laser beam in a ring pattern, and thus the sealing lid 9 iswelded to the lid body 3 b.

By the laser welding, as shown in FIG. 7, a welding mark (welding spot)9 a where the sealing lid 9 and the lid body 3 b are fixed exists in aring shape inside the outermost edge of the plurality of grooves 8 (theouter edge of the predetermined region R1), i.e., at the pouring hole 7side of the grooves 8. At this time, the sealing lid 9 is disposed suchthat the entire outer edge of the sealing lid 9 is located inside theoutermost edge of the plurality of grooves 8 (the outer edge of thepredetermined region R1), i.e., at the pouring hole 7 side of thegrooves 8.

Note that, similarly to the above-described formation of the grooves 8,in the above welding of the sealing lid 9, the entire container 3 oronly the upper portion thereof is made an enclosed space and theatmosphere in the enclosed space is reduced in pressure when the sealinglid 9 is welded. In the case where the relevant exhaust velocity is highor the ultimate vacuum is high, a large quantity of electrolyte willleak out from the pouring hole 7, and thus it is essential to controlreduced atmosphere in a range of 10 kPa to 30 kPa. For example, theexhaust system is controlled with a pressure of 20 kPa as a targetedvalue.

Subsequently, the sealing lid 9 is scanned with a laser beam in a ringpattern in a reduced-pressure atmosphere and is welded as describedabove. Similarly to the above-described formation of the grooves 8, as alaser beam scanning method, a method using a scanner such as a galvanoscanner is preferable because high-speed laser beam scanning is possiblewith the method. However, depending on the scanning speed, a method ofrotating the work body of the container 3, or a method of moving anoptical system using a moving mechanism such as a robot may be used.

Here, the case where a continuous wave laser (CW laser) is used as theaforementioned laser beam, and the case where a pulse laser beam is usedas the aforementioned laser beam are described with reference to FIG. 8.In FIG. 8, the welding mark 9 a formed by CW laser beam irradiation isshown on the upper side, and a welding mark 9 b formed by pulse laserbeam irradiation is shown on the lower side. Note that the CW laser beamis a temporally continuous laser beam, and the aforementioned pulselaser beam is a temporally discontinuous laser beam.

As shown in FIG. 8, the welding mark 9 a formed by CW laser beamirradiation is a single continuous line, but the welding mark 9 b formedby pulse laser beam irradiation includes a weld defect K1. In thewelding by a pulse laser, because the pulse energy is temporallydiscontinuous, the melting time is short, and when a laser pulse withweak laser energy is radiated even once, the welding mark (weldingbeads) 9 b is significantly affected by the laser pulse. Consequently,the weld defect K1 tends to occur,

On the other hand, in the welding by a CW laser, the melting time ofmetal is relatively long, and a metal molten pool continuously moves,and thus the welding mark 9 a as a processing mark is not significantlyaffected even the power varies somewhat. In addition, even when theabsorption rate of the laser beam varies in accordance with the surfaceconditions of the metal as a welding target, the welding mark 9 a is notaffected much for the same reason as described above. Therefore, evenwith a disturbance factor, when a CW laser is used for welding,irregularity in the welding mark 9 a is little, and thus extremelystable welded joint may be obtained. Note that also for the formation ofthe grooves 8, a CW laser is preferably used as described above.

In addition, because the pulse laser has a relatively high peak powerand thus is widely used for welding process, however, in the welding bya pulse laser, the melting time of metal as a processing object isshort, the molten mark becomes discontinuous (what is called a patchworkmark). Therefore, a weld defect such as a splash or a blow hole tends tooccur, and the reliability as a joint is significantly low.Consequently, in many cases, a welded joint by a pulse laser cannot beused for vehicle mount application, which requires high welding quality.

In addition, laser welding by a pulse laser has another problem, thatis, low productivity. Specifically, the welding speed can be improved upto only several tens mm/s at the maximum, and the throughput is low, andthus it is difficult to improve productivity. On the other hand, byusing a CW laser beam for welding, specifically using a solid statelaser such as a fiber laser or a disk laser, which .is capable ofoscillating with continuous output power in the order of several kW,reliability and productivity of the welding can be improved.

As described above, according to the present embodiment, the pluralityof grooves 8 extending in parallel along the outer edge of the pouringhole 7 of the container in which an electrolyte has been poured areformed by irradiating the predetermined region R1 surrounding theperiphery of the pouring hole 7 with a laser; the sealing lid 9 isplaced on the formed grooves 8 in such a manner as to close the pouringhole 7; and the placed sealing lid 8 is fixed to the container 3 bylaser welding, and thus any electrolyte remaining in the periphery ofthe pouring hole 7 is removed because of the heat generated by the laserirradiation as the grooves 8 are formed, and the sealing lid 9 is weldedto the container 3 after the removal of the electrolyte. Consequently, adefect occurrence due to the electrolyte remaining in the vicinity ofthe pouring hole 7 is prevented, and quality of the seal welding of thepouring hole 7 is improved, and thus high quality and high reliabilityof the secondary battery 1 may be achieved. In addition, the secondarybattery 1 can be manufactured with a high yield.

Furthermore, the electrolyte remaining in the periphery of the pouringhole 7 enters the grooves B, and thus spreading of the remainingelectrolyte over a wide area is prevented, and the influence of theremaining electrolyte on the subsequent process of the laser welding maybe reduced. Therefore, a defect occurrence due to the remainingelectrolyte in the vicinity of the pouring hole 7 is securely prevented,and thus quality of the seal welding for the pouring hole 7 can befurther improved.

In addition, the plurality of grooves 8 are formed by irradiating thepredetermined region R1 in the periphery of the pouring hole 7 with alaser beam in a helical pattern along he outer edge of the pouring hole7, and thus each groove 8 extending in parallel along with the outeredge of the pouring hole 7 can be formed in a short time. Thus, themanufacturing time of the secondary battery 1 may be reduced.

In addition, the grooves 8 are successively formed from the inside tothe outside with the pouring hole 7 as the center, therefore, comparedwith successive forming of the grooves from the outside to the inside,the remaining electrolyte may be securely removed from the periphery ofthe pouring hole 7. Consequently, a defect occurrence due to theremaining electrolyte in the vicinity of the pouring hole 7 is moresecurely prevented.

When the predetermined region R1 is irradiated with a laser beam fromthe inside to the outside, a phenomenon occurs in which the electrolyteremaining in the periphery 25 of the pouring hole 7 moves from theinside to the outside, and thus moves to the outside region of thepredetermined region R1, i.e., the region that is not involved in thelaser welding of the sealing lid 9 to the container 3. On the otherhand, when the predetermined region R1 is irradiated with a laser beamfrom the outside to the inside, s a phenomenon occurs in which theelectrolyte remaining in the periphery of the pouring hole 7 moves fromthe outside to the inside, and thus moves to the region that is involvedin the laser welding of the sealing lid 9 to the container 3, i.e., thevicinity of the pouring hole 7, and gathers into large drops, therebymaking it difficult for a laser beam to operate. Consequently, by thelaser beam irradiation from the inside to the outside, the remainingelectrolyte may be more securely removed from the periphery of thepouring hole 7, and thus a defect occurrence due to the remainingelectrolyte in the vicinity of the pouring hole 7 is more securelyprevented.

Note that, although the electrolyte is forced to move from the inside tothe outside by the laser beam irradiation, some of the electrolyte mayremain (for example, some of the electrolyte may return along thegrooves a in a helical shape). Now, after the electrolyte is forced tomove to the outside of the predetermined region R1 completely, weldingis performed inside the outermost edge of the plurality of grooves a(the outer edge of the predetermined region R1), and thus the frequencyof occurrence of a weld failure may be further reduced. Some of theremaining electrolyte returns inwards by capillary action when thesealing lid 9 is placed on the relevant grooves 8 of the lid body 3 b,however, a plurality of walls (walls formed by the grooves 8) arepresent in the radial direction and the electrolyte is absorbed by thegrooves in the circumferential direction, and thus hardly reach theinnermost of the grooves.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A method of manufacturing a secondary batterycomprising: forming a plurality of grooves by laser irradiation in apredetermined region surrounding a periphery of a pouring hole of acontainer in which an electrolyte has been poured, the plurality ofgrooves extending in parallel along an outer edge of the pouring hole;placing a sealing lid on the formed plurality of grooves in such amanner as to close the pouring hole; and fixing the placed sealing lidto the container by laser welding.
 2. A method of manufacturing asecondary battery according to claim 1, wherein the grooves are formedby irradiating the predetermined region with a laser beam in a helicalpattern along the outer edge of the pouring hole.
 3. A method ofmanufacturing a secondary battery according to claim 1, wherein thegrooves are successively formed from an inside to an outside with thepouring hole as a center.
 4. A method of manufacturing a secondarybattery according to claim 1, wherein continuous wave laser beamirradiation is used for the laser welding.